1. Field of the Invention
The present invention relates to a manufacturing method for a semiconductor device and a semiconductor device manufactured according to the manufacturing method. The xe2x80x9csemiconductor devicexe2x80x9d in this specification refers to an electrooptical device such as a liquid crystal display device or a light emitting device and an electronic device using them as a display portion.
2. Description of the Related Art
According to techniques widely employed in recent years, an amorphous semiconductor layer formed on an insulator, particularly, a glass substrate is crystallized, crystalline semiconductor layers are thus obtained, and thin-film transistors (which hereinbelow will be referred to as xe2x80x9cTFTsxe2x80x9d) are manufactured using the crystalline semiconductor layers as active layers. In addition, TFT electrical characteristics have rapidly been improved in recent years.
According to the recent technical advancement, signal-processing circuits of various types, which had been externally mounted using ICs or the like, initially, can be manufactured by using TFTs. Consequently, display devices in which a pixel portion and driver circuits therefor are formed integrally on the substrate have been realized. The displays using a reduced number of components are small and lightweight, and enable a significant manufacturing cost reduction to be implemented. As such, research and development in this field are widely advancing.
TFTs presently used are represented by amorphous silicon TFTs (each of which hereinbelow will be referred to as xe2x80x9ca-Si TFTxe2x80x9d) and polysilicon TFTs (each of which hereinbelow will be referred to as xe2x80x9cp-Si TFTxe2x80x9d). The a-Si TFTs are formed using the aforementioned amorphous semiconductor layer as an active layer, and the p-Si TFTs are formed using the aforementioned crystalline semiconductor layer as an active layer. Compared to the a-Si TFT, the p-Si TFT is superior in various aspects such as significantly high field-effect mobility. Thus, p-Si TFTs have high performance sufficient to form driver circuits of display devices of the type as described above.
However, since transistors used in IC chips or the like are formed on monocrystal silicon, the transistors have even higher electrical characteristics, and the electrical characteristics can be obtained uniformly. In comparison, the p-Si TFT has the semiconductor layer made from an aggregation of numerous crystal grains. While crystalline conditions are sufficient, respectively, electrical characteristics are significantly inferior because of, for example, variation in the orientation boundaries among the crystal grains (grain boundaries). Cases can occur in which a p-Si TFT is formed with an active layer containing a large number of grain boundaries, and variation occurs in the electrical characteristics because of variation in the number of grain boundaries or in the orientation of adjacent crystal grains. In other words, even in a case where TFTs of the same size are manufactured, and voltages of the same magnitude are applied to electrodes, respectively, variation still occurs in, for example, values of currents.
Operational amplifier circuits and differential amplifier circuits are given as representative circuits formed using transistors. These circuits include a current mirror circuit. As shown in FIG. 2A, the current mirror circuit is configured using two transistors 201 and 202, and is characterized in that a drain current I1 flowing through the transistor 201 is identical with a drain current I2 flowing through the transistor 202.
For example, an operational prerequisite condition of the current mirror circuit is that the transistors 201 and 202 are identical in characteristics. Even when the two transistors with variation in characteristics operate, since the condition of I1=I2 is not always ensured, the transistors do not function as an intended circuit. As such, ordinarily, transistors used to form a current mirror circuit are configured using identical materials in terms of, for example, the channel length and channel width. FIG. 2B is a diagram of an example layout of a practical current mirror circuit formed on a substrate.
FIG. 2C shows the configuration of a differential amplifier circuit using this current mirror circuit as an active load. In the circuit, when different potentials are applied to input terminals (In1 and In2), operation is performed satisfying the condition of I1=I2+I3 by utilizing the above current mirror circuit. In the operation, a potential difference between signals input to the input terminals In1 and In2 is amplified, and a waveform generated through the amplification can be obtained from an output terminal (Out) of the circuit. Also in this case, the circuit operates on the prerequisite condition that TFTs 211 to 214 are mutually identical in the electrical characteristics.
In practice, however, as long as the electrical characteristics vary in the p-Si TFT, even when the devices are arranged to have the same sizes, the variation cannot be suppressed. Consequently, the transistors are not suitable for manufacturing the circuit as described above.
Techniques for crystallizing an amorphous semiconductor layer include a technique in which a CW (continuous wave) laser is unidirectionally operated, and laser light is irradiated onto a semiconductor layer. According to this technique, crystal is grown continuously along the operation direction, and monocrystal is thus formed extending long in the operation direction. This technique is considered to enable crystal containing substantially no grain boundaries at least in the direction of the TFT. In this case, the crystal grains have a composition close to that of monocrystal, thereby being imparted with high electrical characteristics and uniformity.
Nevertheless, however, peeling-off can occur with a semiconductor layer deposited on a substrate during the irradiation of CW laser light thereto. When peeling of a semiconductor layer has occurred in a portion of the substrate, removal processing is performed on the semiconductor layer if possible to continue the manufacturing steps such that a semiconductor layer is re-formed. In this case, however, losses are inevitably involved due to the increase in the number of manufacturing steps. Moreover, according to a recent manufacturing method using a large substrate, since a large number of devices can be formed at a time on the substrate, even a loss of a single substrate results in a loss of a plurality of devices.
The present invention is made in view of the problems described above, and an object thereof is to provide a method for efficiently forming a circuit such as a current mirror circuit that requires high inter-device consistency by using polysilicon thin-film transistors (p-Si TFTs).
According to the present invention, after a semiconductor layer is formed on a substrate, first semiconductor islands are formed by a patterning process. Then, the first semiconductor islands are crystallized or are enhanced in crystallinity according to laser irradiation, and second semiconductor islands are then formed by a patterning process. The second semiconductor island is used at a later step as an active layer of a TFT.
A single or a plurality of second semiconductor islands are formed from the first semiconductor island. Particularly, the present invention is characterized in that a single first semiconductor island is used to form second semiconductor islands that are respectively used as active layers for TFTs for which high consistency is required, specifically for all TFTs constituting, for example, one current mirror circuit, one differential amplifier circuit, or one operational amplifier circuit. Hereinbelow, the terminology xe2x80x9cunitary circuitxe2x80x9d generally refers to one circuit containing all the TFTs for which particularly high consistency is required among semiconductor circuits or a configuration portion equivalent thereto. However, the unitary circuit can include TFTs for which particularly high consistency is not required. Thus, active layers of all the TFTs constituting one unitary circuit are formed from one first semiconductor island.
In addition, either the laser-light scanning direction or the shape of the first semiconductor island is determined so that, upon laser light irradiation onto the first semiconductor island, when a laser light spot has reached an end portion of the first semiconductor island, the laser light spot and the first semiconductor island contact at one point as viewed from either the obverse surface or reverse surface of the substrate. For example, laser light is scanned along a path so that a laser light spot first contacts one point of the summit of the first semiconductor island. Alternatively, when the scanning direction has already been determined, the shape of the first semiconductor island is determined so that a laser light spot first contacts one point of the summit of the first semiconductor island. Even when either a portion or the entirety of the periphery of the first semiconductor island is curved, the scanning direction of laser light or the shape of the first semiconductor island is determined so that a laser light spot and the end portion of the first semiconductor island first contact at one contact point. According to the above-described arrangement, when crystallization having an orientation rate of (100) plane develops from the one point at which the laser light spot has first contacted, and laser irradiation to the first semiconductor island is completed, the orientation rate of the (100) plane in the first semiconductor island can be increased.
In addition, as shown in FIG. 21A, scanning may be performed so that a laser light spot first contacts one point of the summit of the first semiconductor island. In the case shown in FIG. 21A, a laser light spot moves in the direction shown by arrows, and contacts summits 2104, 2105, and 2106 of a first semiconductor island 2101. Thereafter, the crystallization proceeds in the directions of arrows shown in FIG. 21B. Consequently, as shown in FIG. 21C, a crystallized first semiconductor layer 2107 is obtained.
Meanwhile, regions 2108 and 2109 of FIG. 21C are shown as regions poor in crystallinity, in which the second semiconductor islands are not preferably formed. Subsequent to the processing described above, patterning is performed, and a second semiconductor island 2110 is thus obtained, as shown in FIG. 21D.
Thus, TFTs are formed using as active layers one or a plurality of second semiconductor islands formed from the first semiconductor island crystallized as described above. Therefore, it is possible to make the TFTs uniform in characteristics as compared with ordinary TFTs. Consequently, a semiconductor circuit including the unitary circuit such as the above-described current mirror circuit, differential amplifier circuit, or operational amplifier circuit can be formed on a substrate by using the TFTs.
A description will be given of structures of the present invention below.
According to the present invention, there is provided a manufacturing method for a semiconductor device, comprising:
forming an amorphous semiconductor layer on a substrate;
patterning the amorphous semiconductor layer into a desired shape to form first semiconductor islands and markers;
irradiating laser light converged into an elliptical or a rectangular shape to a region including the first semiconductor islands while performing scanning relatively to the substrate to crystallize the first semiconductor islands;
patterning the crystallized first semiconductor islands into desired shapes, and forming second semiconductor islands; and
forming thin-film transistors using the second semiconductor islands as active layers and configuring a circuit by using the thin-film transistors,
wherein active layers of all of thin-film transistors included in a unitary circuit included in the semiconductor device are formed of any one of the crystallized first semiconductor islands.
According to the present invention, there is provided the manufacturing method for a semiconductor device, comprising:
forming an amorphous semiconductor layer on a substrate;
forming a metal-containing layer on the amorphous semiconductor layer, and obtaining a first crystalline semiconductor layer by heat treatment;
patterning the first crystalline semiconductor layer into a desired shape to form first semiconductor islands and markers;
irradiating laser light converged into an elliptical or a rectangular shape onto a region including the first semiconductor islands while performing scanning relatively to the substrate to obtain the first semiconductor islands constituted of second crystalline semiconductor layers;
patterning the first semiconductor islands constituted of the second crystalline semiconductor layers into desired shapes to form second semiconductor islands; and
forming thin-film transistors using the second semiconductor islands as active layers, and configuring a circuit by using the thin-film transistors,
wherein the second semiconductor islands serving as active layers of all of thin-film transistors included in a unitary circuit included in the semiconductor device are formed of any one of the first semiconductor islands constituted of the second crystalline semiconductor layers.
In the manufacturing method for a semiconductor device of the present invention, all the thin-film transistors are disposed so that charge movement directions in channel formation regions thereof are consistently arranged parallel or equivalent thereto.
In the manufacturing method for a semiconductor device of the present invention, the unitary circuit is any one of a current source, a current mirror circuit, a differential amplifier circuit, and an operational amplifier circuit.
In the manufacturing method for a semiconductor device of the present invention, the laser light is oscillated from any one of a continuous-wave solid laser, a gas laser, and a metal laser.
In the manufacturing method for a semiconductor device of the present invention, the laser light is oscillated from one laser selected from the group consisting of a continuous-wave YAG laser, YVO4 laser, YLF laser, YAlO3 laser, glass laser, ruby laser, alexandrite laser, and Ti:sapphire laser.
In the manufacturing method for a semiconductor device of the present invention, the laser light is oscillated from one laser selected from the group consisting of a continuous-wave excimer laser, Ar laser, Kr laser, and CO2 laser.
In the manufacturing method for a semiconductor device of the present invention, the laser light is oscillated from one laser selected from the group consisting of a continuous-wave helium-cadmium laser, copper vapor laser, and gold vapor laser.
According to the present invention, there is provided a semiconductor device, wherein:
an amorphous semiconductor layer is formed on a substrate;
the amorphous semiconductor layer is patterned into a desired shape to form first semiconductor islands and markers;
laser light converged into an elliptical or a rectangular shape is irradiated to a region including the first semiconductor islands while performing scanning relatively to the substrate to crystallize the first semiconductor islands;
the crystallized first semiconductor islands are patterned into desired shapes and second semiconductor islands are formed;
thin-film transistors using the second semiconductor islands as active layers are formed to configure a circuit by using the thin-film transistors; and
the second semiconductor islands serving as active layers of all of thin-film transistors included in a unitary circuit included in the semiconductor device are formed of any one of the crystallized first semiconductor islands.
According to the present invention, there is provided the semiconductor device, wherein:
an amorphous semiconductor layer is formed on a substrate;
a metal-containing layer is formed on the amorphous semiconductor layer to obtain a first crystalline semiconductor layer by heat treatment;
the first crystalline semiconductor layer is patterned into a desired shape to form first semiconductor islands and markers;
laser light converged into an elliptical or a rectangular shape is irradiated onto a region including the first semiconductor islands while performing scanning relatively to the substrate to obtain the first semiconductor islands constituted of second crystalline semiconductor layers;
the first semiconductor islands constituted of the second crystalline semiconductor layers are patterned into desired shapes to form second semiconductor islands;
thin-film transistors using the second semiconductor islands as active layers are formed to configure a circuit by using the thin-film transistors; and
the second semiconductor islands serving as active layers of all of thin-film transistors included in a unitary circuit included in the semiconductor device are formed of any one of the first semiconductor islands constituted of the second crystalline semiconductor layers.
According to the present invention, there is provided the semiconductor device which has a circuit configured using a plurality of thin-film transistors, comprising one or a plurality of unitary circuits, wherein the second semiconductor islands serving as active layers of all of thin-film transistors included in the unitary circuit are synchronously formed by patterning one first semiconductor island into a desired shape.
According to the present invention, there is provided the semiconductor device which has a circuit configured using a plurality of thin-film transistors, comprising one or a plurality of unitary circuits, wherein:
the second semiconductor islands serving as active layers of all of thin-film transistors included in the unitary circuit are synchronously formed by patterning one first semiconductor island into a desired shape; and
all the thin-film transistors included in the unitary circuit are disposed so that charge movement directions in channel formation regions thereof are consistently arranged parallel or equivalent thereto.
According to the present invention, there is provided the semiconductor device which has a circuit configured using a plurality of thin-film transistors, comprising one or a plurality of unitary circuits, wherein:
the second semiconductor islands serving as active layers of all of thin-film transistors included in the unitary circuit are synchronously formed by patterning one first semiconductor island into a desired shape; and
all the thin-film transistors included in the unitary circuit are disposed so that charge movement directions in channel formation regions thereof are consistently arranged parallel with a scanning direction of laser light that is irradiated to crystallize the first semiconductor islands or equivalent thereto.
According to the present invention, there is provided the semiconductor device, wherein the unitary circuit is any one of a current source, a current mirror circuit, a differential amplifier circuit, and an operational amplifier circuit.